Re: [Haskell-cafe] State & nested structures

2010/10/29 Dupont Corentin :

Of course in module A I'm calling some functions of module B. I'd like to know if it's possible, in a function of type SA, to call a function of type SB, without actually executing the State SB. I just wanna tell him "Hey look, you can construct a SA from a SB like this!"

Also, I can't manage to write the more generic function SB x ->  SA x.

You can have a class that expresses the operations upon some B, e.g. class MonadB m where getB :: m b and then implement that class for both SA and SB. Or you can implement MonadTrans in order to write the more generic function SB x -> SA x. Possibly both but preferably the former imho.